After
wounding and the death of non-woody parts, the tree's defense depends greatly
on strengthening existing boundaries and building new boundaries. Mycorrhizae
[M] are what we call ephemeral meaning that they come fast and they go
fast. How fast, we are not sure, but being the nonwoody structure that
they are, it is unlikely that they live for more than one year. Within
the stage from aging to dying it is common to see new mycorrhizae forming
close to others. If we look closely at the nonwoody root [NR] we will see
a cup [C] (doughnut like with a hole in the center) that holds the structure.
The hole is closed as the mycorrhiza begins to die {mycorrhiza-singular;
mycorrhizae-plural}. ROOT-INFECTING pathogens find it very easy to gain
entrance at this point when closure does not take place. Two examples of
conditions that might prevent closure are SOIL COMPACTION AND FLOODING
(over watering). What happens with a leaf is the leaf will die first and
then the abscission layer or zone is formed and then the leaf is shed.
What the word shed means is that a boundary separates the leaf from the
tree. To shed by no means is to cast away. Mycorrhizae are shed as well.
However the mycorrhizae begins to die first and then the boundary begins
to form. They are not able to fall away and they are digested in place.
If compaction and flooding kill the mycorrhizae then the boundary will
not form! It is easy to say that there is at least as much root tissue
formed and shed below ground as leaves above. Mycorrhizae is a very major
part of the vitality of the tree system.
Diagrams from The Desk of John A. Keslick Jr.
Call us for other ORGANIC FACT SHEETS on pruning and other tree care information.
John A. Keslick Jr.
Tree Biologist
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Text & Graphics Copyright © 1997 Keslick & Son Modern Arboriculture